Fuel injector for blast furnace

ABSTRACT

An injector for a combustible mixture, to be discharged across the tuyeres of a blast furnace, has an inner tube for the passage of a stream of liquid fuel and an outer tube traversed by a flow of oxidizing gas (air or oxygen) under pressure, the fuel stream passing through an obliquely perforated insert which directs it along helicoidal paths onto the peripheral tube wall to form a layer progressing toward the discharge end of the injector. Between that discharge end and the insert, the fuel layer is subjected to radially outwardly acting pressure from a gas, which may be branched off the surrounding flow of oxidizing gas, admitted generally tangentially into the inner tube through a set of nozzles extending skew to the tube axis, thereby reducing the thickness of the fuel layer. The surrounding gas flow, also set in swirling motion by passing through a fluted or perforated ring, impinges upon this thinned fuel layer at the discharge end and atomizes it. The exit speed of the fuel stream may be increased by disposing an inwardly pointing axial cone in the discharge end of the inner tube, leaving a narrow annular channel through which the fuel and its entraining gas pass into contact with the surrounding gas flow exiting through a narrow gap between the tubes.

Elite States atent [191 Metz et a1.

[4 1 Aug. 27, 1974 FUEL INJECTOR FOR BLAST FURNACE [75] Inventors: Paul Metz, Luxembourg; Victor Koch; Robert Schockmel, all of Esch/Alzette, Luxembourg [73] Assignee: Acieries Reunies de B rha -yestdaa s. S.A.-ARBED, Luxembourg, G.D. de Luxembourg [22] Filed: Jan. 29, 1973 [21] App]. No.: 327,835

[30] Foreign Application Priority Data Jan. 28, 1972 Luxembourg 64674 [52] US. Cl 431/8, 75/42; 239/425, 431/181 [51] Int. Cl. F23c 5/00 [58] Field of Search 431/8, 4, 187,181; 266/41, 29, 30; 239/425, 426, 430, 431; 75/44, 42

[56] References Cited UNITED STATES PATENTS 1,511,019 10/1924 Bluemel 431/187 2,239,025 4/1941 Vigneault 431/187 2,764,455 9/1956 Seibel 239/430 3,197,305 7/1965 Carlson. 75/42 3,758,090 9/1973 Kaisha 266/41 Primary ExaminerJ0hn J, Camby Attorney, Agent, or Firm-Karl F. Ross; Herbert Dubno [57] ABSTRACT An injector for a combustible mixture, to be discharged across the tuyeres of a blast furnace, has an inner tube for the passage of a stream of liquid fuel and an outer tube traversed by a flow of oxidizing gas (air or oxygen) under pressure, the fuel stream passing through an obliquely perforated insert which directs it along helicoidal paths onto the peripheral tube Wall to form a layer progressing toward the discharge end of the injector. Between that discharge end and the insert, the fuel layer is subjected to radially outwardly acting pressure from a gas, which may be branched off the surrounding flow of oxidizing gas, admitted generally tangentially into the inner tube through a set of nozzles extending skew to the tube axis, thereby reducing the thickness of the fuel layer. The surrounding gas flow, also set in swirling motion by passing through a fluted or perforated ring, impinges upon this thinned fuel layer at the discharge end and atomizes it. The exit speed of the fuel stream may be increased by disposing an inwardly pointing axial cone in the discharge end of the inner tube, leaving a narrow annular channel through which the fuel and its entraining gas pass into contact with the surrounding gas flow exiting through a narrow gap between the tubes.

20 Claims. 9 Drawing Figures -li has 3 321 m 1 mm I Pmmapwcz mm 2 3.832.121 A E HEATED L U/D FUEL PATENTEDAUBNIQH m w z 3.882J21 FUEL INJECTOR FOR BLAST FURNACE FIELD OF THE INVENTION Our present invention relates to an injector for the introduction of a combustible mixture into blast furnaces used in the production of molten metals.

BACKGROUND OF THE INVENTION 1 To improve the efficiency of blast furnaces and to reduce the required quantity of solid fuels such as coke, liquid combustibles are frequently utilized. Often, however, difficulties are experienced in insuring adequate dispersion of the liquid fuel in the hot-air blast flowing at high velocity through the tuyeres of the furnace. It has therefore already been proposed to atomize the preferably preheated liquid fuel by high-pressure gas admitted into an expansion chamber in the interior of an injector, the energy of the gas flow being used in part to disperse the liquid and in part to convert the resulting droplets into a mist issuing at high speed from y the injection nozzle. Structural complications arise from the need for generating the necessary high gas pressure; moreover, variations in that pressure may seriously impair the performance of the injectors.

OBJECTS OF THE INVENTION SUMMARY OF THE INVENTION We realize the foregoing objects by the use of a tube provided with a discharge end and connected at its opposite end to a supply of liquid fuel to be atomized, such as extra-heavy hydrocarbon oil, the interior of this tube being provided with guide means such as a perforated insert directing an entering, preferably preheated fuel stream toward the inner tube wall as a peripheral layer progressing, preferably by a helicoidal motion, toward the discharge end. At an intermediate location between the guide means and the discharge end, a first flow of gas is admitted into the tube with a velocity component directed toward the discharge end and with exertion of radially outward pressure upon the peripheral fuel layer in the tube whereby the thickness of that layer is reduced; a second flow of gas is trained at the discharge end upon the exiting fuel layer entrained by the first flow whereby the fuel is dispersed in the accompanying gas. At least the second gas flow should be of oxidizing character (air or oxygen); the first one could be of the same nature, and may in fact be split off that second flow, but can also be a combustible fluid such as natural gas. Both gas flows may be under a relatively low pressure, e.g., on the order of 4 kg/cm (i.e., about four atmospheres gauge).

According to another feature of our invention, a conduit delivering the second gas flow forms a preferably coaxial outer tube or jacket about the fuel tube and defines therewith an annular gap which converges on the axis of the latter tube around the discharge end thereof for training that gas at an acute angle onto the fuel/gas stream exiting therefrom. Part of the gas traversing an annular duct formed by these two tubes, and terminating at that gap, may be branched off by a set of nozzles, preferably skew to the tube axis, to form the first gas flow entering the interior of the tube to radially compress the fuel layer. Similar flow-guiding means, setting the second gas flow in codirectional swirling motion about the tube axis, may be provided in the annular duct between the tubes downstream of the nozzle array.

The vortical motion of the fuel and gas within the inner tube may be further intensified by the provision of inclined ribs or vanes at the discharge end of that tube; these ribs may also be used to support an axially inwardly pointing cone defining with the inner tube a constricted exit channel in the vicinity of the aforementioned annular gap whose width is advantageously adjustable by a relative axial shifting of the two nested tubes.

We have found that best results are obtained, in terms of an effective distribution of the incoming fuel stream over the inner tube wall, by providing the perforated tubeinsert with a flat, smooth upstream surface confronting the entrance end of thetube and with a set of perforations, skew to the tube axis, for imparting the desired helicoidal motion to the peripheral fuel layer.

BRIEF DESCRIPTION OF THE DRAWING The above and other objects, features and advantages of the present invention will become more readily apparent from the following description, reference being made to the accompanying drawing in which:

FIG. 1 is a diagrammatic axial cross-sectional view through an injector embodying our invention;

FIG. 2 is a cross-sectional view of a guide ring, taken on the line II II of FIG. 1';

FIG. 2A is a view similar to FIG. 2, showing a modified guide ring;

FIG. 3 is a side-elevational view of the guide ring shown in FIG. 2;

FIG. 4 is a top view of a perforated insert, taken on the line IV IV of FIG. 1;

FIG. 5 is a side-elevational view of the insert shown in FIG. 4;

FIG. 6 is a cross-sectional view of the discharge end of the injector, taken on the line VI VI of FIG. 1;

FIG. 7 is a cross-sectional view of the fuel chamber of the injector taken on line VII VII of FIG. 1; and

FIG. 8 is an overall, schematic view showing the emplacement of a set of injectors according to our invention in a blast furnace.

SPECIFIC DESCRIPTION In FIGS. 1-7 we have shown an injector 20 receiving liquid fuel, such as a heavy oil, through a central pipe 310 which is coaxially surrounded by an outer barrel 101 carrying an oxidizing gas such as air or oxygen at a relatively low pressure of several atmospheres gauge. The body of the injector 20 comprises a pair of coaxially nested tubes, i.e., an outer tube and an inner tube 300, threadedly connected at 340, 350 to conduits 101 and 310, respectively. Tubes 100 and 300 define between them an annular duct 200 containing, near its downstream end, a ring 210' provided with bores 21] lying skew to the tube axis A. A cylindrical insert 320 is seated near the entrance end of tube 300, being held in position between a shoulder 302 of that tube and the adjoining extremity of pipe 310, and is formed with a set of inclined bores 321 which also lie skew to the axis A in the same sense as the bores 211 of ring 210. As specifically illustrated in FIGS. 3 and 5, bores 211 and 321 include angles of 30 with a direction (here verti cal) parallel to axis A when viewed at right angles to a vertical plane containing their own axis; their upper and lower ends lie on two circles C and D, centered on axis A, which are the larger and the smaller base of a frustocone with a 30 vertex angle (see FIG. 5). The upper surface 322 of insert 320, confronting the oncoming preheated fuel stream (arrow B in FIG. I), is flat and smooth.

Between the upstream region of insert 320 and the downstream region of guide ring 210, tube 300 is penetrated by at least two symmetrically positioned nozzles 331 (best seen in FIG. 7) which open into the interior 330 or this tube with an inclination similar to that of the bores 211 and 321 so as to deviate part of the flow E of low pressure oxidizing gas from duct 200 to fuel chamber 330. The fuel stream, which by virtue of the aforedescribed inclination of the bores 321 is directed with helicoidal motion onto the inner tube wall to form a layer thereon, is further accelerated by this gas flow toward an annular channel 340 at the exit end of the tube, this channel being defined by the tube mouth and by a conical guide member 332 held centered on axis A by a set of vanes 333. The vanes, as best seen in FIG. 6, are inclined to set the outflowing fuel-gas stream in rotation about the axis in the same sense (here counterclockwise) as imparted to them by the bores 321 and the nozzles 331. On exiting from the channel 340, this composite stream encounters the tubular flow of the remaining gas from duct 200 which leaves that duct through a narrow annular gap 220 of frustoconical shape whose generatrices converge on the axis A beyond the exit at an angle of 30. It will be noted that the gas passing through gap 220 strikes the exiting stream from channel 340 at a large acute angle, thus nearly orthogonally, as the two fluid volumes revolve in the same counterclockwise sense about the axis.

The nozzles 331 enter the chamber330 nearly tangentially but open into that chamber at locations radially inward of the inner surface of the annular fuel layer which forms on the wall of tube 300 and has been indicated at F in FIG. 7. Thus, the gas discharged by these nozzles into the chamber 330 acts radially outwardly upon this fuel layer F to compress it into a thin film as it travels toward the exit channel 340. The body of liquid remains substantially coherent at this stage and does not mix with the accompanying gas. The outer gas stream striking that film at the tube mouth disintegrates it into a mass of small droplets dispersed throughout the surrounding gas volume so as to produce a fine mist that burns with practically no residue; the geometry of the exit end of the injector causes this mist to spread from the end face 221 of the injector in the form of an expanding cone with partial vaporization of the fuel particles distributed throughout the gas volume.

The conical insert 332, which further increases the exit speed of the fuel/gas stream, is not essential and may be omitted in some instances.

As shown in FIG. 2A, guide ring 210 may be replaced by a modified ring 210A having external flutes 211A in lieu of bores 211 of ring 2P0. These flutes, of course, have the same inclination as the bores, lying skew to the axis A at an angle of about 30 in the present instance.

The necessary fluidtightness at the junction of conduits 101 and is ensured by the provision of an annular gasket 111 as illustrated in FIG. 1. The gasket enables a certain relative axial adjustment of tubes 100 and 300 to vary the effective width of gap 220.

The gas stream entering the fuel chamber 330 by nozzles 33] or similar adjutages need not be branched off the flow (arrows E) passing through duct 200 but could also be supplied by a separate source. In the latter instance, if desired, a hydrocarbon gas could be used to increase the ratio of combustible fluid in the exiting composite stream.

In FIG. 8 we have illustrated part of a blast furnace 10 provided with the usual set of tuyeres 12 which are supplied by air or oxygen under pressure via a manifold 13 and open into a hearth 14 below a bosh 11. Injectors 20, as described above, open into respective tuyeres 12, at an acute angle to their axes, just ahead of the tuyere outlets to introduce theirfuel/air or fuel/oxygen mixture into an air blast feeding a flame in the hearth 14. The ferrous melt produced by the furnace accumulates at 15, together with accompanying slag.

In a practical realization of an injector as shown in FIG. 1, but with omission of the cone 332, extra-heavy fuel oil preheated to C was introduced into tube 300 under a pressure of 6 kg/cm at a rate of 70 grams per cubic meter of hot air blown through the associated tuyeres under a pressure of about one atmosphere gauge. Air at 25C was delivered through conduit 101 at a pressure of four atmospheres gauge. Complete combustion with a short, stable flame was achieved.

We claim:

1. A fuel injector for a blast furnace, comprising:

a tube provided with a discharge end and connected at its opposite end to a supply of liquid fuel to be atomized;

guide means in said tube directing an entering stream of said fuel toward the tube wall as a rotating peripheral layer progressing toward said discharge end;

feed means between said guide means and said discharge end opening into said tube at a location inward of the inner boundary of said layer for admitting into said tube a first flow of gas with a velocity component toward said discharge end and with exertion of radially outward pressure upon said layer to reduce the thickness thereof; and

conduit means terminating at said discharge end for training a second flow of gas upon the fuel layer entrained by said first flow and exiting from said inner tube, at least said second flow of gas being of oxidizing character, thereby dispersing the fuel in the gas admixed therewith.

2. A fuel injector as defined in claim 1 wherein said conduit means forms an annular gap, converging on the tube axis, around said discharge end for training said second flow of gas at an acute angle onto the exiting fuel/gas stream.

3. A fuel injector as defined in claim 2 wherein said conduit means forms a jacket around said tube, said second flow of gas passing through an annular duct between said tube and said jacket to said gap.

4. A fuel injector as defined in claim 3 wherein said 5. A fuel injector as defined in claim 3, further comprising flow-guiding means in said space for imparting a swirling motion to said second flow of gas ahead of said gap.

6. A fuel injector as defined in claim 3 wherein said tube and said jacket are relatively axially adjustable for varying the effective width of said gap.

7. A fuel injector as defined in claim 3, further comprising an axially inwardly pointing cone at said discharge end for defining with said tube a constricted exit channel for said fuel/gas stream in the vicinity of said gap.

8. A fuel injector for a blast furnace, comprising:

a tube provided with a discharge end and connected at its opposite end to a supply of liquid fuel to be atomized;

guide means in said tube directing an entering stream of said fuel toward the tube wall as a peripheral layer progressing toward said discharge end;

a set of nozzles traversing said tube wall between said guide means and said discharge end for admitting into said tube a first flow of gas with a velocity component toward said discharge end and with exertion of radially outward pressure upon said layer to reduce the thickness thereof; and

conduit means forming a jacket around said tube and defining therewith an annular duct for the conveyance of the second flow of gas to said discharge end, said jacket forming around said discharge end an annular gap converging on the tube axis for training a second flow of gas at an acute angle upon the fuel layer entrained by said first flow and exiting from said inner tube, at least said second flow of gas being of oxidizing character, thereby dispersing the fuel in the gas admixed therewith, said nozzles communicating with said annular duct for branching said first flow of gas off said second flow of gas.

9. A fuel injector as defined in claim 8 wherein said nozzles are skew to the tube axis for imparting a generally helicoidal motion to said first flow of gas.

10. A fuel injector for a blast furnace, comprising:

a tube provided with a discharge end and connected at its opposite end to a supply of liquid fuel to be atomized;

guide means in said tube directing an entering stream of said fuel toward the tube wall as a peripheral layer progressing toward said discharge end;

feed means between said guide means and said discharge end for admitting into said tube a first flow of gas with a velocity component toward said discharge end and with exertion of radially outward pressure upon said layer to reduce the thickness thereof;

conduit means forming a jacket around said tube and defining therewith an annular duct for the conveyance of a second flow of gas to said discharge end, said jacket forming around said discharge end an annular gap converging on the tube axis for training said second flow of gas upon the fuel layer entrained by said first flow and exiting from said inner tube, at least said second flow of gas being of oxidizing character, thereby dispersing the fuel in the gas admixed therewith; and

flow-guiding means in said space for imparting a v swirling motion to said second flow of gas ahead of said gap. 11. A fuel injector as defined in claim 10 wherein said guide means comprises an insert in said tube with perforations skew to the tube axis for imparting a generally helicoidal motion codirectional with said swirling motion to said layer.

12. A fuel injector for a blast furnace, comprising:

a tube provided with a discharge end and connected at its opposite end to a supply of liquid fuel to be atomized;

guide means in said tube directing an entering stream of said fuel toward the tube wall as a peripheral layer progressing toward said discharge end;

feed means between said guide means and said discharge end for admitting into said tube a first flow of gas with a velocity component toward said discharge end and with exertion of radially outward pressure upon said layer to reduce the'thickness thereof; and

conduit means forming a jacket around said tube and defining therewith an annular duct for the conveyance of a second flow of gas to said discharge end, said jacket forming around said discharge end an annular gap converging on the tube axis for training said second flow of gas upon the fuel layer entrained by said first flow and exiting from said inner tube, at least said second flow of gas being of oxidizing character, thereby dispersing the fuel in the gas admixed therewith, said tube and said jacket being relatively axially adjustable for varying the effective width of said gap.

13. A fuel injector for a blast furnace, comprising:

a tube provided with a discharge end and connected at its opposite end to a supply of liquid fuel to be atomized;

guide means in said tube directing an entering stream of said fuel toward the tube wall as a peripheral layer progressing toward said discharge .end;

feed means between said guide means and said discharge end for admitting into said tube a first flow of gas with a velocity component toward said discharge end and with exertion of radially outward pressure upon said layer to reduce the thickness thereof; 7

conduit means forming a jacket around said tube and defining therewith an annular duct for the conveyance of a second flow of gas to said discharge end, said jacket forming around said discharge end an annular gap converging on the tube axis for training said second flow of gas at an acute angle upon the fuel layer entrained by said first flow and exiting from said inner tube, at least said second flow of gas being of oxidizing character, thereby dispersing the fuel in the gas admixed therewith; and

an axially inwardly pointing cone at said discharge end for defining with said tube a constricted exit channel for said fuel/gas stream in the vicinity of said tap.

14. A fuel injector as defined in claim 13 wherein said cone is connected with said tube by radial ribs inclined to help set said fuel/gas stream in rotation about the tube axis.

15. A fuel injector as defined in claim 1 wherein said guide means comprises an insert in said tube with a flat, smooth upstream face confronting the entering fuel stream and with a set of perforations skew to the tube axis for imparting a generally helicoidal motion to said layer.

16. A method of generating a combustible mixture for injection into a blast furnace, comprising the steps of:

feeding a stream of liquid fuel through a tube;

distributing said stream as a rotating peripheral layer on the inner wall surface of said tube;

flattening said layer by admitting a first gas flow into said tube at a location inward of the inner boundary of said layer with a radially outward pressure component and with a velocity component directed towardan exit end of the tube for entrainment of said layer toward same; and

admixing an oxidizing second gas flow at said exit end with the resulting fuel/ gas stream for dispersing the fuel in the accompanying gas.

17. A method as defined in claim 16 wherein said first and second gas flows are under a pressure on the order of several atmospheres gauge.

18. A method as defined in claim 16 wherein said first and second gas flows are of the same composition.

19. A method as defined in claim 16 wherein said liquid fuel is preheated before entering said tube.

20. A fuel injector for a blast furnace, comprising:

a tube provided with a discharge end and connected at its opposite end to a supply of liquid fuel to be atomized;

an insert in said tube directing an entering stream of said fuel toward the tube wall as a peripheral layer progressing toward said discharge end, said insert being provided with a flat, smooth upstream face confronting the entering fuel stream and with a set of perforations skew to the tube axis for imparting a generally helicoidal motion to said layer;

feed means between said insert and said discharge end for admitting into said tube a first flow of gas with a velocity component toward said discharge end and with exertion of radially outward pressure upon said layer to reduce the thickness thereof; and

conduit means terminating at said discharge end for training a second flow of gas upon the fuel layer entrained by said first flow and exiting from said inner tube, at least said second flow of gas being of oxidizing character, thereby dispersing the fuel in the gas admixed therewith. 

1. A fuel injector for a blast furnace, comprising: a tube provided with a discharge end and connected at its opposite end to a supply of liquid fuel to be atomized; guide means in said tube directing an entering stream of said fuel toward the tube wall as a rotating peripheral layer progressing toward said discharge end; feed means between said guide means and said discharge end opening into said tube at a location inward of the inner boundary of said layer for admitting into said tube a first flow of gas with a velocity component toward said discharge end and with exertion of radially outward pressure upon said layer to reduce the thickness thereof; and conduit means terminating at said discharge end for training a second flow of gas upon the fuel layer entrained by said first flow and exiting from said inner tube, at least said second flow of gas being of oxidizing character, thereby dispersing the fuel in the gas admixed therewith.
 2. A fuel injector as defined in claim 1 wherein said conduit means forms an annular gap, converging on the tube axis, around said discharge end for training said second flow of gas at an acute angle onto the exiting fuel/gas stream.
 3. A fuel injector as defined in claim 2 wherein said conduit means forms a jacket around said tube, said second flow of gas passing through an annular duct between said tube and said jacket to said gap.
 4. A fuel injector as defined in claim 3 wherein said feed means comprises a set of nozzles traversing said tube wall and communicating with said annular duct, said first flow of gas being branched off said second flow of gas by said nozzles.
 5. A fuel injector as defined in claim 3, further comprising flow-guiding means in said space for imparting a swirling motion to said second flow of gas ahead of said gap.
 6. A fuel injector as defined in claim 3 wherein said tube and said jacket are relatively axially adjustable for varying the effective width of said gap.
 7. A fuel injector as defined in claim 3, further comprising an axially inwardly pointing cone at said discharge end for dEfining with said tube a constricted exit channel for said fuel/gas stream in the vicinity of said gap.
 8. A fuel injector for a blast furnace, comprising: a tube provided with a discharge end and connected at its opposite end to a supply of liquid fuel to be atomized; guide means in said tube directing an entering stream of said fuel toward the tube wall as a peripheral layer progressing toward said discharge end; a set of nozzles traversing said tube wall between said guide means and said discharge end for admitting into said tube a first flow of gas with a velocity component toward said discharge end and with exertion of radially outward pressure upon said layer to reduce the thickness thereof; and conduit means forming a jacket around said tube and defining therewith an annular duct for the conveyance of the second flow of gas to said discharge end, said jacket forming around said discharge end an annular gap converging on the tube axis for training a second flow of gas at an acute angle upon the fuel layer entrained by said first flow and exiting from said inner tube, at least said second flow of gas being of oxidizing character, thereby dispersing the fuel in the gas admixed therewith, said nozzles communicating with said annular duct for branching said first flow of gas off said second flow of gas.
 9. A fuel injector as defined in claim 8 wherein said nozzles are skew to the tube axis for imparting a generally helicoidal motion to said first flow of gas.
 10. A fuel injector for a blast furnace, comprising: a tube provided with a discharge end and connected at its opposite end to a supply of liquid fuel to be atomized; guide means in said tube directing an entering stream of said fuel toward the tube wall as a peripheral layer progressing toward said discharge end; feed means between said guide means and said discharge end for admitting into said tube a first flow of gas with a velocity component toward said discharge end and with exertion of radially outward pressure upon said layer to reduce the thickness thereof; conduit means forming a jacket around said tube and defining therewith an annular duct for the conveyance of a second flow of gas to said discharge end, said jacket forming around said discharge end an annular gap converging on the tube axis for training said second flow of gas upon the fuel layer entrained by said first flow and exiting from said inner tube, at least said second flow of gas being of oxidizing character, thereby dispersing the fuel in the gas admixed therewith; and flow-guiding means in said space for imparting a swirling motion to said second flow of gas ahead of said gap.
 11. A fuel injector as defined in claim 10 wherein said guide means comprises an insert in said tube with perforations skew to the tube axis for imparting a generally helicoidal motion codirectional with said swirling motion to said layer.
 12. A fuel injector for a blast furnace, comprising: a tube provided with a discharge end and connected at its opposite end to a supply of liquid fuel to be atomized; guide means in said tube directing an entering stream of said fuel toward the tube wall as a peripheral layer progressing toward said discharge end; feed means between said guide means and said discharge end for admitting into said tube a first flow of gas with a velocity component toward said discharge end and with exertion of radially outward pressure upon said layer to reduce the thickness thereof; and conduit means forming a jacket around said tube and defining therewith an annular duct for the conveyance of a second flow of gas to said discharge end, said jacket forming around said discharge end an annular gap converging on the tube axis for training said second flow of gas upon the fuel layer entrained by said first flow and exiting from said inner tube, at least said second flow of gas being of oxidizing character, thereby dispersing the fuel in the gas admixed therewith, said tube and Said jacket being relatively axially adjustable for varying the effective width of said gap.
 13. A fuel injector for a blast furnace, comprising: a tube provided with a discharge end and connected at its opposite end to a supply of liquid fuel to be atomized; guide means in said tube directing an entering stream of said fuel toward the tube wall as a peripheral layer progressing toward said discharge end; feed means between said guide means and said discharge end for admitting into said tube a first flow of gas with a velocity component toward said discharge end and with exertion of radially outward pressure upon said layer to reduce the thickness thereof; conduit means forming a jacket around said tube and defining therewith an annular duct for the conveyance of a second flow of gas to said discharge end, said jacket forming around said discharge end an annular gap converging on the tube axis for training said second flow of gas at an acute angle upon the fuel layer entrained by said first flow and exiting from said inner tube, at least said second flow of gas being of oxidizing character, thereby dispersing the fuel in the gas admixed therewith; and an axially inwardly pointing cone at said discharge end for defining with said tube a constricted exit channel for said fuel/gas stream in the vicinity of said tap.
 14. A fuel injector as defined in claim 13 wherein said cone is connected with said tube by radial ribs inclined to help set said fuel/gas stream in rotation about the tube axis.
 15. A fuel injector as defined in claim 1 wherein said guide means comprises an insert in said tube with a flat, smooth upstream face confronting the entering fuel stream and with a set of perforations skew to the tube axis for imparting a generally helicoidal motion to said layer.
 16. A method of generating a combustible mixture for injection into a blast furnace, comprising the steps of: feeding a stream of liquid fuel through a tube; distributing said stream as a rotating peripheral layer on the inner wall surface of said tube; flattening said layer by admitting a first gas flow into said tube at a location inward of the inner boundary of said layer with a radially outward pressure component and with a velocity component directed toward an exit end of the tube for entrainment of said layer toward same; and admixing an oxidizing second gas flow at said exit end with the resulting fuel/gas stream for dispersing the fuel in the accompanying gas.
 17. A method as defined in claim 16 wherein said first and second gas flows are under a pressure on the order of several atmospheres gauge.
 18. A method as defined in claim 16 wherein said first and second gas flows are of the same composition.
 19. A method as defined in claim 16 wherein said liquid fuel is preheated before entering said tube.
 20. A fuel injector for a blast furnace, comprising: a tube provided with a discharge end and connected at its opposite end to a supply of liquid fuel to be atomized; an insert in said tube directing an entering stream of said fuel toward the tube wall as a peripheral layer progressing toward said discharge end, said insert being provided with a flat, smooth upstream face confronting the entering fuel stream and with a set of perforations skew to the tube axis for imparting a generally helicoidal motion to said layer; feed means between said insert and said discharge end for admitting into said tube a first flow of gas with a velocity component toward said discharge end and with exertion of radially outward pressure upon said layer to reduce the thickness thereof; and conduit means terminating at said discharge end for training a second flow of gas upon the fuel layer entrained by said first flow and exiting from said inner tube, at least said second flow of gas being of oxidizing character, thereby dispersing the fuel in the gas admixed therewith. 